Method for synchronising a steering wheel and steered wheels of a motor vehicle

ABSTRACT

The invention relates to a method and a device for synchronizing the position (LH) of the steering handle and the steering angle (LH) which has been set at the steered vehicle wheels. By means of a control device it is possible to set a relationship function or steering characteristic curve ( 21, 22, 23 ) between the steering handle position (LH) and the steering angle (LW). After the control device has been activated, the instantaneous handle position (LH) and the instantaneous steering angle (LW) are compared taking into account the instantaneously set relationship function, and in the case of a deviation (S) in position a relative adjustment is carried out in order to reduce the deviation (S) in position between the handle position (LH) and the steering angle (LW).

The invention relates to a method for synchronizing a steering handleand steered vehicle wheels, in particular in the case of a motorvehicle, according to the preamble of claim 1. In addition, theinvention relates to a device which is particularly suitable for themethod.

Steering systems with a variable relationship function between theposition of the steering wheel and the steering angle which has been setat the steered vehicle wheels are affected.

For example, DE 196 01 826 A1 presents a steering system in which asteering gear component which controls the steered vehicle wheels isconnected mechanically via a variable ratio gear unit both to a steeringwheel and to an automatically controlled electric motor. Accordingly, achange in steering angle of the steered wheels is determined in eachcase by the superimposition of the change in the position of thesteering wheel and the change in position of the electric motor. Inprinciple any relationship function between the handle position andsteering angle can then be set by means of a control device which isassigned to the electric motor.

Similar conditions apply in steering systems which operate according tothe “steer-by-wire” concept. Such a steering system is described, forexample, in DE 100 21 903 A1. In said document, a steering wheelactivates a steering angle setpoint value transmitter. A steering angleactual value transmitter and a, for example, electric, actuating motorwhich is provided for adjusting steering are assigned to the steeredvehicle wheels, said actuating motor being controlled by a closed-loopcontrol device as a function of a setpoint value/actual value comparisonof the steering angle. As a result, the steering angle of the steeredvehicle wheels therefore follows the predefined steering angle of thesteering wheel.

If the steering system is faulty, in particular if the power supply isinterrupted or switched off, according to DE 100 21 903 A1 a steeringcolumn which can be disconnected by means of a clutch is providedbetween the steering wheel and the steered vehicle wheels, with theclutch being opened during the normal steering mode so that therelationship function between the steering angle which is set at thesteered vehicle wheels and the angle of rotation of the steering wheelduring normal operation is determined solely by the closed-loop controldevice.

In such steering systems, the steering wheel can be activated even ifthe open-loop or closed-loop control device is not operating, if theengine of the vehicle is switched off and/or if the electrical powersupply of the vehicle has failed. However, in such a case therelationship function between the steering wheel angle and the steeringangle of the steered vehicle wheels is not given in accordance with thesteering characteristic curve stored in the open-loop or closed-loopcontrol device but rather there is a mechanical coupling of the steeringhandle and steered vehicle wheels to a mechanically predefinedrelationship function. In the case of DE 196 01 826 A1 this is therelationship function of the positive coupling which is present betweenthe steering wheel and the steered vehicle wheels when the electricmotor is deactivated. In the case of DE 190 21 903 A1 this is therelationship function of the positive coupling which is brought aboutbetween the steering wheel and steered vehicle wheels when the clutch isclosed.

If the abovementioned positive coupling is effective at a time at whichthe steered vehicle wheels assume a steering angle which is differentfrom the straight-ahead position, and the steering handle accordinglyassumes a position which is different from the normal position, thecorrelation between the steered vehicle wheels and the steering handlewhich is mentioned at the beginning then generally no longer occurssince the relationship function between the position of the handle andthe steering angle is different when the positive coupling is activethan during normal operation of the steering system. This can lead to asituation in which the normal position of the steering handle no longercoincides with the straight-ahead position of the steered vehicle wheelswhen the positive coupling is maintained between the steering handle andsteered vehicle wheels.

Even if the position of the handle is changed when the control device isdeactivated, and if a normal driving mode with actuated control deviceis subsequently resumed, the correlation between the position of thehandle and the steering angle is eliminated. This is due to therelationship function between the position of the handle and thesteering angle which is changed in the normal operating mode incomparison with the relationship function given by the steeringmechanism when the control device is deactivated.

The object of the invention is to permit, with a steering system of thetype mentioned at the beginning, automatic synchronization of theposition of the steering handle and the steering angle which has beenset at the steered vehicle wheels.

This object is achieved according to the invention by means of thecharacterizing features of patent claims 1 and 12.

The invention is based on the general idea of performing a possiblynecessary or desirable synchronization of the steering handle andsteered vehicle wheels after the control device has been activated. Thiscan either be activation after a failure or activation by the electricpower supply being switched on again by the driver, for example by meansof the ignition. In this activated state, the control device can detecta deviation in position and if appropriate perform a relativeadjustment. This relevant adjustment leads to a situation in which theposition of the handle and the steering angle correspond to one anothertaking into account the instantaneously valid relationship function.

Advantageous developments emerge from the dependent patent claims.

It is advantageous if the relative adjustment takes place only if aninterrogation criterion is fulfilled after the or during the activationof the control device. The interrogation criterion may be, for example,a driving state variable of the vehicle or a variable describing anoperator control activity of the driver. It is basically also possibleto perform this relative adjustment after the vehicle has started withthe vehicle stationary. However, a driver who does not yet know thesteering system or does not known it in such a situation, could besurprised. The driver could then feel that the steering system is nolonger following him. Moreover, dangers which arise when carelessmaintenance or repair work is carried out can be reduced. For example, aperson could reach into the movement area of the steered vehicle wheelsor place his head there and be trapped by the relative adjustment if atthe same time another person switches on the ignition. Since therelative adjustment does not take place until the other interrogationcriterion has been fulfilled, this danger is ruled out.

It is possible to provide here that, in particular in the case of avehicle longitudinal velocity which is lower than a predefinablevelocity threshold value, the relative adjustment is to be carried outonly while the steering handle (8) is being moved manually by thedriver. This measure ensures that the synchronization is carried out byrelative adjustment only when the driver is carrying out steeringactivities and in particular when low longitudinal velocities of thevehicle are present (for example less than 5 km/h) or the vehicle isstationary. The driver can cope with relative adjustments verysatisfactorily if he carries out steering activities himself. In thiscontext he must always make slight corrections, but this is hardlyperceived during the steering process so that he always has thesensation that the steering system of the vehicle is reacting to hissteering activity and following him. Since large steering angle changesin the steered vehicle wheels and corresponding large deflectionmovements of the steering handle are often necessary directly after avehicle starts in order to maneuver the vehicle out of a car park ontothe carriageway, the synchronization may be carried out in a way whichis virtually unnoticed by the driver and completely at a low velocity.

It is also expedient if the relative adjustment takes place in anincremental cyclical fashion, in particular in the case of a vehiclelongitudinal velocity which is higher than a predefinable velocitythreshold value, and one adjustment step is carried out per adjustmentcycle until the deviation in position corresponds to approximately zero.Cyclically carrying out adjustment steps provides the possibility ofcarrying out the relative adjustment in a way which is adapted to thedriving state of the vehicle and the operator control activity of thedriver.

In this context, the reduction in the deviation in position peradjustment cycle can be limited to, or defined as, a predefinedpercentage of the respective current deviation in position, as a resultof which deviation in position approaches zero asymptotically. It hasbeen found in trials that such a reduction in deviation in positionwhich has a profile similar to an e function is very pleasant for thedriver.

In order to reduce the deviation in position in a time period which isacceptable to the driver, a predefinition is expediently made of anadjustment time period after whose expiry the deviation in position musthave reached a value which in absolute terms is less than or equal to adeviation threshold value, which may be approximately zero.

So that the driver has sufficient time to accordingly adjust theposition of the handle during the relative adjustment there isadvantageously provision for the relative adjustment to take place withan adjustment velocity at the steered vehicle wheels which is predefinedor limited to a maximum value. This means that the gradient of theadjustment path which is covered during the relative adjustment islimited or predefined to a fixed value. The driver can then calmlycorrect the position of the handle so that the desired course of thevehicle is restored. The adjustment speed at the steered vehicle wheelsmay be, for example, between 0.1 and 1.0° per second. This results, inaccordance with the currently set relationship function, in the handlespeed with which the driver has to adjust or reposition the steeringhandle in order to hold his course.

In a further advantageous embodiment of the method there is provision inthe case of a vehicle longitudinal velocity which is less than apredefinable velocity threshold value for the relative adjustment totake place only if the direction of a change in the handle positionwhich is carried out manually by the driver corresponds to the directionin which the relative adjustment at the steered vehicle wheels is totake place. A relative adjustment at the steered vehicle wheels to theright is thus carried out only if the driver moves the steering handlein the direction corresponding to a deflection of the wheel to theright, that is to say if, for example, he turns the steering handle tothe right, and this applies correspondingly to the relative adjustmentto the left.

The deviation in position can be determined in such a way that after thecontrol device (13) has been activated the setpoint position of thesteering handle (8) which corresponds to the instantaneous steeringangle for the instantaneously set steering transmission ratio isdetermined, wherein the deviation in position results from thedifference between the instantaneous handle position and the setpointhandle position.

The relative adjustment may be carried out as a function of parameters.In particular, the adjustment velocity may depend on one or moreparameters which describe the current vehicle movement dynamic state orsome other vehicle state. Possible parameters are, for example: a manualforce which is effective at the steering handle, the instantaneousdeflection of the steering handle out of its normal positioncorresponding to the straight-ahead position on the steered vehiclewheels, the instantaneous deflection of the steered vehicle wheels outof their straight-ahead position, the absolute value of the deviation inposition, a variable which characterizes the lateral dynamics orlongitudinal dynamics of the vehicle (for example the longitudinalvelocity of the vehicle) and/or the time.

Moreover, with respect to preferred features of the invention referenceis to be made to the claims and to the subsequent description of thedrawing which describes in more detail particularly preferredembodiments of the invention, and protection is claimed not only for thefeature combinations which are described expressly but also for intheory any desired combinations of the described features. In thedrawing:

FIG. 1 shows an embodiment of a steering system in which the steeredvehicle wheels are mechanically connected to a steering wheel and to aself-locking electric motor via a variable ratio gear unit,

FIG. 2 shows an exemplary embodiment of a steering system which operatesaccording to the steer-by-wire concept, and

FIG. 3 is a diagram illustrating various steering characteristic curveswhich each specify a relationship function between the position of thesteering handle and the steering angle of the steered vehicle wheels,with possible synchronization measures being also represented by way ofexample.

According to FIG. 1, a motor vehicle (which is otherwise not illustratedin more detail) has steerable front wheels 1 which are connected to oneanother via track rods 2 with a connecting rod 3 to form a commonsteering activation system.

The connecting rod 3 is forcibly mechanically coupled via a gearmechanism 4 to a steering shaft 5 which has a drive connection, on theone hand, via a variable ratio gear unit 6 to a steering wheel shaft 7on which a steering handle which is embodied as a steering wheel 8 isarranged so as to be fixed in terms of rotation and, on the other hand,via a shaft 9 to a self-locking electric motor 10. The superimpositionof rotational movements of the steering wheel shaft 7 and of the shaft 9therefore determines the rotational movement of the steering shaft 5.Accordingly, the rotational movements of the two shafts 7 and 9 aresuperimposed, with the rotational movement of the steering shaft 5resulting from this superimposition.

The position LH of the steering wheel 8 is sensed by a handle sensor. Inthe exemplary embodiment illustrated according to FIG. 1, the steeringwheel shaft 7 or the steering wheel 8 interacts with a rotational angletransmitter 11 which forms the handle sensor and which senses therotational adjustment of the steering wheel 8 or steering wheel shaft 7.Alternatively or additionally an instantaneous sensor could also be usedas a handle sensor.

A steering angle transmitter is provided for sensing the steering anglewhich is instantaneously set at the steered vehicle wheels. For thispurpose, the connecting rod 3 interacts with a position transducer 12which senses the displacement in the connecting rod 3 and thus theaverage steering angle LW of the front wheels 1. It goes without sayingthat instead of or in addition to the position transducer 12 it wouldalso be possible to use, for example, angle sensors or other suitablesensors.

The rotational angle transmitter 11 and position transducer 12 areconnected to corresponding inputs of an electronic control device 13which actuates the electric motor 10 or a driver circuit (notillustrated) of this motor 10 which is in turn connected fixedly interms of rotation to the shaft 9 and drives the latter accordingly. Asstated above, the rotational movement of the steering wheel shaft 7 issuperimposed on the rotational movement of the shaft 9 to form therotational movement of the steering shaft 5 which is then converted intoa change in steering angle by means of the gear mechanism 4, theconnecting rod 3 and the track rod 2.

In the example in FIG. 2, the connecting rod 3 is connected via the gearmechanism 4 to a steering shaft 15 which can be disconnected and coupledin terms of movement by means of a clutch 16 so that the steering wheel8 which is arranged on the steering shaft 15 so as to be fixed in termsof rotation to the end of the steering shaft 15 which is remote from thetransmission is mechanically connected in terms of movement to theconnecting rod 3, and accordingly to the steerable front wheels 1, onlywhen the clutch 16 is closed, and is mechanically decoupled in terms ofmovement from the steerable front wheels when the clutch 16 is open. Theconnecting rod 3 is connected in terms of drive to a, for example,electric, self-locking-free actuating motor 17. Said actuating motor 17,or its driver circuit (not illustrated), is controlled by means of anelectronic closed-loop control device 18 which is assigned at the inputend a handle sensor, which is assigned to the steering wheel 8 or thesteering-wheel-end part of the steering shaft 15 and is embodied as arotational angle transmitter 19, and to a displacement sensor 20 forsensing the displacement of the connecting rod 3 and correspondingly ofthe central steering angle LW of the front wheels. As is described inconjunction with FIG. 1, in this exemplary embodiment also the handlesensor could alternatively or additionally have a torque sensor, and anangle sensor could additionally or alternatively be used to measure thesteering angle LW.

Moreover, the closed-loop control device 18 is connected at the outputend to the clutch 16 or to an actuating motor (not illustrated) of theclutch 16 which is held open by the closed-loop control device 18 in thenormal steering operating mode.

In the normal steering operating mode, the closed-loop control device 18carries out a setpoint/actual value comparison for the steering angleLW. The steering angle setpoint value is determined in the closed-loopcontrol device 18 by means of the handle position LH sensed by therotational angle transmitter 19. The rotational angle actual value ismeasured by the displacement transducer 20. The closed-loop controldevice 18 controls the actuating motor 17 as a function of thedifference between the steering angle setpoint value and steering angleactual value so that as a result the steering adjustment of thesteerable front wheels 1 follows the predefined values of the steeringwheel 8.

The closed-loop control device 18 can, in determining the steering anglesetpoint value, take into account parameters such as adjustment valueswhich can be set by the driver or, for example, parameters describingthe vehicle movement dynamic state of the vehicle such as thelongitudinal velocity of the vehicle. As a result, various functions forthe relationship between the handle position LH and the steering angleLW—which can also be referred to as steering characteristic curves—canbe set as a function of parameters. It is also conceivable in thiscontext for the driver to be able to select in each case a relationshipfunction as a current relationship function from a plurality ofpredefined relationship functions or steering characteristic curves.

When there are faults which adversely affect the steering system in thenormal operating mode and when the electric power supply of theclosed-loop control device 18 is switched off, for example after thevehicle has been parked, the clutch 16 closes so that the steerablefront wheels 1 are controlled in a conventional mechanical fashion bymeans of the steering shaft 15 using the steering wheel 8, with theself-locking-free actuating motor 17 also being moved. When the clutchis closed, another relationship function from that during the normaloperating mode of the steering system is then given.

The synchronization of the handle position LH with the position of thesteered vehicle wheels 1 will be explained below in more detail withreference to FIG. 3. In the diagram in FIG. 3, the steering angle LW isplotted at the steered vehicle wheels by means of the steering wheelangle LH. By way of example relationship functions or steeringcharacteristic curves 21 to 23 which can be set in the normal operatingmode of the steering systems described with respect to FIGS. 1 and 2 areillustrated.

As is shown by way of example by the steering characteristic curves 21to 23, the straight-ahead position of the front wheels 1, i.e. LW=0, isalways assumed precisely when the steering wheel 8 assumes its centralposition in which LH=0.

It is possible to change or switch over from one steering characteristiccurve to another steering characteristic curve, for example from thefirst steering characteristic curve 21 to the second steeringcharacteristic curve 22, even while the vehicle is traveling. In thiscontext, the first steering characteristic curve 21 is displacedincrementally toward the second steering characteristic curve 22 untilthe relationship function given by the second steering characteristiccurve 22 has been reached. In the switching over process, a plurality ofsteering characteristic curves between the first and second steeringcharacteristic curve are, as it were, successively activated in order toaccustom the driver slowly to the changing steering behavior of thevehicle.

It will now be assumed that the current handle position LH has the valueLH₁ and the second steering characteristic curve 22 is currently activeso that the steering angle LW₁ is set in the normal operating mode.Consequently, the first point P₁ on the second steering characteristiccurve 22 is obtained. It will also be assumed that when the position ofthe steering is unchanged the vehicle is shut down so that the electricpower supply is switched off and that in this shut-down state thesteering handle is moved so that the handle position LH changes.

When the vehicle is deactivated or the engine of the vehicle is switchedoff and/or the electric on-board power system is switched off thesteering automatically goes into a special operating mode correspondingto a “fall back level”. In the case of a steering system as in FIG. 1this is equivalent to the electric motor 10 remaining deactivatedirrespective of the rotational travel of the steering wheel 8. In thecase of a steering system in FIG. 2, the clutch 16 is closed so that thesteering wheel 8 is forcibly mechanically coupled to the steered frontwheels 1.

However, when the electric power supply is switched off a specialoperating characteristic curve 24 which is different from the secondsteering characteristic curve 22, is predefined by the mechanicalconfiguration of the steering system and constitutes, for example astraight line but in a modification of this it may in principle alsohave other profiles. The special operating characteristic curve 24 isillustrated by dashed lines in FIG. 3.

By way of the rotation of the steering wheel 8 with the electronic powersupply switched off starting from that position of the steering wheel 8and of the steered vehicle wheels 1 which is defined by the first pointP₁ an assignment function is obtained according to the special operatingcharacteristic curve 24 which passes through the first point P₁. As aresult, the synchronization between the handle position LH and steeringangle LW is cancelled because the special operating characteristic curvedoes not pass through the coordinate jump 0. At a steering angle LW ofzero, the steering wheel angle is unequal to zero, and vice versa.Correspondingly, during operation at the fall back level there is nosynchronization between the steering wheel 8 and steered front wheels 1,i.e. the steered front wheels 1 assume their straight-ahead positionwhen the steering wheel 8 is not located in the central position or havea position which deviates from the straight-ahead position if thesteering wheel 8 is in its central position.

It will be assumed that when the power supply is switched off the secondpoint P₂ on the special operating characteristic curve 24 will have beenreached before the steering system can return to its normal operatingmode. If the electric power supply is, for example, switched on again bystarting the vehicle, the relationship function which was set last andwhich corresponds to the second steering characteristic curve 22 isactivated or set. However, the second point P₂ does not lie on thesteering characteristic curve 22 so that a relative adjustment betweenthe steering wheel 8 and steered vehicle wheels 1 has to take place forsynchronization purposes.

After the open-loop or closed-loop control device has been activated byswitching on the electric power supply, the deviation S in position isdetermined. At first, a setpoint handle position LH_(Sol1) of thesteering handle which corresponds to the instantaneous steering angleLW₂ with the instantaneously set relationship function according to thesteering characteristic curve 22 is determined, with the deviation S inposition being obtained from the difference between the instantaneoushandle position LH₂ and the setpoint handle position LH_(Sol1). The signof the deviation S in position indicates the direction in which thesteered vehicle wheels 1 are to be moved during the relative adjustment.

For example there is now provision here for the necessary relativeadjustments for synchronization purposes to be carried out only if aninterrogation criterion is fulfilled.

Firstly, the longitudinal velocity of the vehicle serves as theinterrogation criterion with the present embodiment of the method. Ifthe longitudinal velocity of the vehicle is larger in absolute termsthan a predefined velocity threshold value, which may be, for example,between 0.5 and 5 km/h, the relative adjustment takes place cyclically.In each adjustment cycle, an adjustment step is carried out so that thedeviation S in position is reduced after each adjustment step.

The absolute value of the adjustment step which is carried out in eachadjustment cycle is obtained from a permanently predefined percentage ofthe absolute value of the deviation S in position which is then currentin this adjustment cycle. The absolute value of the adjustment stepsaccordingly decreases in each adjustment cycle. However, thesynchronization speed, that is to say the gradient of the relativeadjustment, is limited to a maximum value in order to avoid rapidlydecreasing relative adjustment movements which the driver cannotcompensate without difficulty by correcting the handle position LH. Therelative adjustment then takes place very slowly, for example withsynchronization speeds between 0.1 and 1.0° per second at the steeredvehicle wheels.

In one modified embodiment variant it is also possible to predefine anadjustment time period after whose expiry the deviation S in positionmust be less than a predefined deviation threshold value by an absolutevalue, or equal to said predefined deviation threshold value, in orderto avoid long deviations in position being present. The deviationthreshold value may be, for example, approximately zero.

In the case of a longitudinal velocity of the vehicle which is lowerthan the predefined velocity threshold value, the relative adjustmenttakes place only while the steering handle 8 is being moved manually bythe driver. Furthermore only a relative adjustment is performed if thedirection of the change in the position of the handle corresponds to thedirection in which the relative adjustment is to be carried out. Thismeans that a relative adjustment at the steered vehicle wheels 1 to theright occurs only when the steering wheel is rotated to the right. Thisapplies correspondingly to a relative adjustment to the left.

This case of a longitudinal velocity of the vehicle which lies below thevelocity threshold value is assumed in FIG. 3.

Starting from the second point P₂, the steering angle LW increases muchless in the direction of the relatively large handle position values LHthan it actually should according to the currently set relationshipfunction in accordance with the second steering characteristic curve 22(arrow 25 in FIG. 3). A slight increase in the steering angle LW iscarried out in order to impart to the driver a functionally capablechange in steering angle which follows its steering wheel movement.

At the third point P₃, the driver switches over the direction ofrotation of the steering wheel 8 so that starting from this position therelationship between the handle position LH and steering angle LWaccording to arrow 27 is given. Here, the steering angle LW is reducedto a greater degree by the superimposed relative adjustment than ispredefined by the change in the handle position and the second steeringcharacteristic curve 22.

Finally, the arrow 27 strikes the second steering characteristic curve22 at the fourth point P₄. Starting from this time, the deviation S inposition is reduced to zero and the relationship function between thesteering angle LW and the handle position LH correspond again to theprofile of the second steering characteristic curve 22.

The gradient of the arrows 25 and 27 may be changeable as a function ofparameters provided that the open-loop control device 13 of the steeringsystem according to FIG. 1 or the closed-loop control device 18 of thesteering system according to FIG. 2 receives, from a correspondingsensor system, data relating to the respective parameters. For example,the deviation with which the steering angle LW is synchronized againwith the handle position LH by the superimposed relative adjustment iscalculated as a function of the longitudinal velocity of the vehicle.Alternatively it would also be possible to take into account othervariables which describe the longitudinal or transverse dynamics of thevehicle, such as the longitudinal acceleration or the transverseacceleration. The current handle position LH, the current steering angleLW or other parameters which describe the state of the vehicle can alsobe taken into account.

1-12. (canceled)
 13. A method for synchronizing the position (LH) of thesteering handle and the steering angle (LW) which has been set at thesteered vehicle wheels (1) for steering with a relationship functionwhich can be set between the handle position (LH) and the steering angle(LW) by means of an open-loop or closed-loop control device (13; 18),wherein after the activation of the open-loop or closed-loop controldevice (13; 18) which follows nonoperation of the open-loop orclosed-loop control device (13; 18) the instantaneous handle position(LH) and the instantaneous steering angle (LW) are compared taking intoaccount the instantaneously set relationship function, and in the caseof a deviation (S) in position a relative adjustment is carried out inorder to reduce the deviation (S) in position between the handleposition (LH) and the steering angle (LW), characterized in that therelative adjustment takes place only if after or during the activationof the open-loop or closed-loop control device (13; 18), aninterrogation criterion is fulfilled in addition to the deviation (S) inposition.
 14. The method as claimed in claim 13, characterized in that,in particular in the case of a vehicle longitudinal velocity which islower than a predefinable velocity threshold value, the relativeadjustment takes place only while the steering handle (8) is being movedmanually by the driver.
 15. The method as claimed in claim 13,characterized in that the relative adjustment takes place in anincremental cyclical fashion, in particular in the case of a vehiclelongitudinal velocity which is higher than a predefinable velocitythreshold value, and one adjustment step is carried out per adjustmentcycle until the deviation (S) in position is approximately zero.
 16. Themethod as claimed in claim 15, characterized in that the reduction inthe deviation (S) in position per adjustment cycle is limited to, ordefined as, a predefined percentage of the respective current deviation(S) in position.
 17. The method as claimed in claim 13, characterized bythe definition of an adjustment time period after whose expiry thedeviation (S) in position has to have reached a value which in absoluteterms is less than or equal to a predefined deviation threshold value.18. Method as claimed in claim 13, characterized in that the relativeadjustment takes place with a synchronization speed at the steeredvehicle wheels (1) which is predefined or limited to a maximum value.19. The method as claimed in claim 13, characterized in that in the caseof a vehicle longitudinal velocity which is less than a predefinablevelocity threshold value, the relative adjustment takes place only ifthe direction of the change in the handle position corresponds to thedirection in which the relative adjustment is to take place.
 20. Themethod as claimed in claim 13, characterized in that after the controldevice (13) has been activated the setpoint position (LH_(Sol1)) of thesteering wheel (8) which corresponds to the instantaneous steering angle(LW) for the instantaneously set steering transmission ratio isdetermined, wherein the deviation (S) in position results from thedifference between the instantaneous handle position (LH_(ist)) and thesetpoint handle position (LH_(Sol1)).
 21. The method as claimed in claim13, characterized in that the relative adjustment takes place as afunction of parameters.
 22. The method as claimed in claim 21,characterized in that the relative adjustment takes place as a functionof a manual force which is effective at the steering wheel (8) and/or ofthe instantaneous deflection of the steering wheel (8) out of its normalposition corresponding to the straight-ahead position of the steeredvehicle wheels (1) and/or of the instantaneous deflection of the steeredvehicle wheels (1) out of their straight-ahead position and/or of theabsolute value of the deviation (S) in position and/or of a variablewhich characterizes the lateral dynamics or longitudinal dynamics of thevehicle and/or of the longitudinal velocity of the vehicle and/or oftime.
 23. A device for carrying out the method as claimed in claim 13,having means (11; 19) for determining the position (LH) of a steeringwheel (8) of a vehicle, having means (12; 20) for determining thesteering angle (LW) of the steered vehicle wheels (1) and having anopen-loop or closed-loop control device (13; 18) for setting thesteering angle (LW) as a function of the position (LH) of the steeringwheel (8) and a relationship function which can be set between thehandle position (LH) and the steering angle (LW), wherein after theopen-loop or closed-loop control device (13; 18) has been activatedfollowing nonoperation it compares the instantaneous handle position(LH) and the instantaneous steering angle (LW) taking into account theinstantaneously set relationship function between the handle position(LH) and steering angle (LW), and in the case of a deviation (S) inposition it carries out a relative adjustment in order to reduce thedeviation (S) in position between the handle position (LH) and thesteering angle (LW), characterized in that the relative adjustment takesplace only if, after or during the activation of the open-loop orclosed-loop control device (13; 18), an interrogation criterion isfulfilled in addition to the deviation (S) in position.